Human visual function declines with age. Much of this decline is associated with neuronal changes in the central visual pathways. The purpose of this proposal is, for the first time A highly experienced, productive, and innovative investigator proposes to determine what changes in the visual system account for age-related declines in visual performance. The central hypothesis is that the most relevant alterations in the system occur in visual cortex rather than in the eye, retina, or LGN. Impressive preliminary results from aged and young monkeys support that contention. An array of related experiments are now proposed to evaluate possible changes in the properties of neurons in primary visual cortex, and possible changes in neurotransmitter expression in cortex, and relate these findings to visual behavior in the same monkeys, as well as to possible alternations in the LGN and eye.